In vehicles of recent years, a control technique of stopping the engine to cause the vehicle to travel through inertia when a torque request is not made by a driver at the time of travelling of the vehicle is being developed in an aim of improving fuel economy, reducing amount of exhaust gas emission, and the like. At the time of inertia travelling, power generation by an alternator is stopped, so that power supply is carried out only with the discharging of the battery. In this case, the supply amount of electricity to a device that is activated with electricity may become insufficient depending on the state of the battery. Thus, a technique that resolves the insufficiency of power supplying amount at the time of inertia travelling is being proposed.
For example, in a method of operating an internal combustion described in patent literature 1, the engine is stopped and the inertia travelling is carried out if the torque request is not made by the driver and an activation prepared state of a system of the portion related to the safety of the vehicle is realized. In a state the inertia travelling is being carried out, the engine is started to supply power if an electric or an electro-hydraulic steering assist device or a brake device that is electrically activated or assisted is not activating normally, or if the energy remaining in a power supply circuit that can activate such devices becomes poor. Thus, the power supplying amount can be ensured even if the power supplying amount to the device that is activated with electricity becomes insufficient, and the inertia travelling can be carried out without destructing the safety.